Field of the Invention
The present invention relates to an image forming apparatus of an electrophotographic system or electrostatic recording system.
Description of the Related Art
A well-known conventional image forming apparatus of an inline color system, such as a laser beam printer, has a configuration in which a plurality of image bearing members are arranged side by side in the rotation direction of an intermediate transfer member. In such an image forming apparatus, a photosensitive drum serving as the image bearing member is uniformly charged with charging means, a toner image is developed with developing means at an electrostatic latent image formed on the photosensitive drum by an exposure device, and the toner image is primary transferred onto the intermediate transfer member. A full-color toner image is then formed on the intermediate transfer member by repeating the same primary transfer with a plurality of colors. Then, the full-color toner image is secondary transferred onto a recording material, and the full-color tone image is permanently fixed to the recording material with fixing means. In this case, the so-called mono-component contact development is used as the developing means. When the image is formed, the electrostatic latent image on the photosensitive drum is developed by bringing a developing roller serving as a developer bearing member into contact with the photosensitive drum. In the non-image-formation period, the developing roller is separated from the photosensitive drum.
The toner (untransferred toner) which has not been transferred onto the transfer material in the secondary transfer process and remains on the intermediate transfer member needs to be removed from the intermediate transfer member. Accordingly, the so-called transfer-synchronized collection system has been suggested for removing the untransferred toner from the intermediate transfer member (see Japanese Patent Application Publication No. H9-50167). Thus, the untransferred toner present on the intermediate transfer member is retransferred to the photosensitive drum during the next primary transfer process by charging the toner to a polarity reversed with respect to that of the regular charged state of the toner with the toner charging means. The toner retransferred to the photosensitive drum is removed with cleaning means such as a cleaning blade.
Further, a method using an electrically conductive brush member and an electrically conductive roller member has been suggested for collecting the untransferred toner present on the intermediate transfer member (referred to hereinbelow, as secondary untransferred toner (Japanese Patent Application Publication No. 2009-205012). More specifically, mechanical scattering, primary collection, and charging of the secondary untransferred toner present on the intermediate transfer member are performed by applying a DC voltage to the brush member.
With such a configuration, the collection can be performed simultaneously with the primary transfer to the next page and the images can be continuously formed without reducing the printing speed. The secondary untransferred toner on the very last page in a series of continuous printing operations is collected with the cleaning blade of the photosensitive drum in the non-image-formation period. The primary collected toner retained at the brush member is then released onto the intermediate transfer member by alternately applying positive and negative voltage to the brush member. Where the amount of the primary collected toner at the brush member is large, as in the case of large number of successive continuous printing operations, the printing is interrupted to obtain a non-image-formation state in order to maintain the toner charging performance of the brush member. The toner accumulated at the brush member is then released. Since such collection of the secondary untransferred toner from the very last page and the collection of the toner by releasing the toner from the brush member are performed in the non-image-formation period, those collection operations are performed when the photosensitive drum and developing roller are separated from each other.